Reply by TopamaxSurvivor

I am not sure of the power out put of alternators in vehicles, but all day use is likely to run your battery down even if the vehicle is running. Deep cycles are very hard on automotive batteries. It should be fine for occasional short period usage.

Keep in mind the inverter needs to located as close to the 12v source as possible. Voltage drop in 12 volt circuits can be excessive and to the point of rendering them useless.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence